Field of the Invention
The present invention relates to a diode, and in particular to a diode required to be high in breakdown voltage and low in ON resistance.
Description of the Background Art
Silicon (Si) has conventionally been adopted as a semiconductor material for fabricating a power semiconductor element. Such performance as a low loss, a high breakdown voltage, and a high operation speed, however, has been approaching to the theoretical limit of a silicon semiconductor element.
A semiconductor greater in band gap than silicon, is called a “wide band gap semiconductor.” Owing to a wide band gap semiconductor, drastic improvement in performance of a power semiconductor element is expected. For example, a wide band gap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN) has attracted attention as a material for a power semiconductor. For example, ON resistance characteristics of a p-n junction diode formed on a free-standing GaN substrate have been reported in Yoshitomo Hatakeyama, Kazuki Nomoto, Naoki Kaneda, Toshihiro Kawano, Tomoyoshi Mishima, Tohru Nakamura, “Over 3.0 GW/cm2 Figure-of-Merit GaN p-n Junction Diodes on Free-Standing GaN Substrates,” IEEE ELECTRON DEVICE LETTERS, Vol. 32, No. 12, pp. 1674-1676, December 2011.